The present invention relates to a method for joining two parts to each other, more specifically, to a method which provides a joined portion with a high level of air tightness.
Conventionally, it has been widely practiced to make two parts by press molding a sheet of steel and join them together, for example, in a manufacturing process of an exhaust muffler used for a small internal combustion engine. As for the exhaust muffler, it is desirable for the joined portion thereof to have a high level of air tightness because a housing made of plastic which surrounds the exhaust muffler could melt due to exposure to high temperature exhaust gas and also the interior of the housing could become contaminated by the exhaust gas if an exhaust gas is leaked from the joined portion. Conventionally, many various measures have been applied to prevent a gas leak from the joined portion, including, for example, repeating the sealing process several times, applying a sealing agent to join surfaces facing each other, brazing an end portion, or inserting a packing material between joined surfaces.
However, those measures as described above have detrimental effects such as an increase in a number of steps in a manufacturing process which results in a cost increase therein.
Accordingly, an object of the present invention is to provide a method for providing a tightly sealed joined portion with a reduced number of operating steps and reduced costs without a reduction in quality. Further, it is also an object of the present invention to provide a unit comprising parts which are joined by the same method.
The above object of the present invention can be accomplished by a method for joining two parts together, the method comprising the steps of: mating a first flange portion extending along an entire periphery of a first part with a second flange portion extending along an entire periphery of a second part; overfolding a margin portion extending along an outer edge of the second flange portion to join the first part and the second part; providing a linear ridge being formed on at least one of the first flange portion, the second flange portion and the margin portion, the linear ridge extending along an entire periphery of the at least one portion and extending toward the first flange portion, the second flange portion or the margin portion which is opposite to the linear ridge in an overfolded state; and compressing the margin portion to plastically deform the linear ridge so as to form a seal between the two parts.
According to the present invention, the linear ridge is strongly compressed against the opposite surface to establish a sealing therebetween and a high level of air tightness can be obtained. Further, since in the present invention, the linear ridge is integrally formed on the part during the forming process thereof, only a overfolding and compressing steps are required to join them, that is, no additional steps and parts are not required. Accordingly, it makes it possible to simplify the operation and to reduce the cost. In addition, since the linear ridge is strongly compressed against the opposite surface, a reliable sealing is ensured along the entire periphery, thereby preventing any reduction in the resultant quality.